There is such a wide range of light bulbs available on the market that it is sometimes difficult to make a choice. It is possible to take into account quantitative elements (energy efficiency, life-time of the bulb) as well as qualitative aspects (quality of light, colour rendition, recycling, etc.). Here is an overview of the different kinds of light bulbs and their energy efficiency patterns.

To reduce your electricity bill, forget filament lamps…

If electricity is used to heat your home and water, doing so represents 80% of your overall electricity consumption. In that case, lighting accounts for an estimated 3%. But if you take heating and hot water out of the equation and focus on home appliances, then lamps and light bulbs use up 14% of the total, less than a fridge and a freezer combined (32%) but as much as the dishwasher (14%), the dryer (14%) and more than an audiovisual equipment (12%). Home lighting thus represents a significant part of a household’s electricity consumption, which justifies the use of more and more energy efficient light bulbs.

Electrical lighting is based on two separate technologies: filament lamps (aka incandescent bulbs)and fluorescent lamps. In the former, a tungsten filament wire is heated until it glows. It is the oldest method and is still widely used today. However it wastes a lot of energy since filament lamps only convert 5 to 8% of the power they use into visible light; the rest gets lost via heat and infrared light. Besides, their life span is limited: barely 1000 hours for a conventional filament bulb.

Halogen bulbs are an improvement from conventional filament lamps. Their higher temperature yields more power; furthermore, they provide an excellent colour rendition and contrary to common beliefs, they have a higher light efficiency than standard incandescent bulbs because they emit a wider segment of the visible light spectrum. Nevertheless, they use up a lot of energy and have a limited life span, barely twice as high as standard filament bulbs, that is about 2000 h.

… and move on to fluorescent bulbs

The marketing of “low-energy light bulbs” coined new terms such as “compact fluorescent lights” (CFL), “discharge lamps” or “energy-saving light bulbs”. They actually all mean the same thing, that is fluorescent lamps. Such lamps have no filament but two electrodes, between which a discharge generates an electric arc in a bulb filled with noble gases, metal fumes (sodium or mercury) and rare earths. Historically, the first examples of this technology are neon tubes, which have been used for illuminated signs since the middle of the last century. Actually, a CFL is nothing more than a fluorescent tube folded on itself so it takes less space.

Compact fluorescent lights offer unquestionable advantages compared to filament lamps: their average life span is ten times longer and they offer higher light efficiency, from 60 to 100 lumens per watt (lm/W) compared to 12 to 20 lm/W for standard bulbs. Finally, they produce much less heat.

How to achieve efficient and economical home lighting

Not all kinds of light bulbs fit all places in your home. For instance, although they are bound to disappear because they use up to much power, filament lamps are ideal for spot-lighting, in the corridor or in the toilets for example. It is easy to compensate their low energy efficiency by combining them to a time-switch or a motion sensor and by using them briefly, only when necessary. Fluorescent lights, on the contrary, are suited for rooms where long-lasting lighting is required, which makes their slight ignition delay less of a problem. However, they have the important disadvantage of containing toxic substances and must be recycled, especially to avoid mercury pollution.

But as far as energy efficiency is concerned, light-emitting diodes or LEDs are undoubtedly the most promising technology. Unfortunately, so far, their colour rendition (measured by the colour rendering index, CRI) is really unsatisfactory: their monochromatic light (be it blue, green or red LEDs) is not adequate for home lighting and research on white LEDs has not advanced enough yet. For the time being, they may only be used at home for ambiance lighting and decoration.